Shelf



FIG. 1 is a front, bottom and left side perspective view of a shelf showing my new design;

FIG. 2 is a rear, top and left side perspective view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a bottom view thereof;

FIG. 5 is a front view thereof;

FIG. 6 is a rear view thereof;

FIG. 7 is a right side view thereof; and,

FIG. 8 is a left side view thereof.

The broken lines show portions of the shelf that form no part of the claimed design. 

CLAIM The ornamental design for a shelf, as shown and described. 